Converters generally have a number of semiconductor components using which, controlled by a suitable control unit, a direct voltage or alternating voltage from a first network applied at the input side may be converted into a direct voltage or alternating voltage of a second network supplied at the output side. For example, a DC/DC converter may have multiple half-bridge circuits connected in parallel to one another at the input side and at the output side.
In addition, input and output capacitors or intermediate-circuit capacitors may be provided for smoothing the input current and the output voltage.
Fault currents may occur in converters. For example, the fault currents may be caused by a reduction in the insulating resistance of the input and output capacitors. This may occur in particular when using ceramic capacitors (MLCC capacitors: multilayer ceramic capacitors), which have a comparatively high sensitivity to mechanical stresses. In addition, a fault current may occur due to defective semiconductor switches if they have an elevated cutoff current in the blocked state.
In particular when using the converter as a DC/DC converter, a shared ground potential is provided for the DC voltage networks connected through the DC/DC converter. To detect a fault current in the DC/DC converter, a fault current detector may therefore be provided between the shared ground potential and the converter circuit of the converter, as is already known from the publication German Published Patent Application No. 10 2008 041 341. Prior to activating the converter, there is a check on whether a fault current between the converter circuit of the converter and the ground potential is present prior to establishing a low-resistance connection between the converter circuit of the converter and the ground potential.
Such a configuration has the disadvantage that a node, which has a fluctuating potential prior to the activation of the converter, is created between the converter circuit of the converter and the ground potential. This may result in undesirable voltage potentials. In addition, shared-mode interference may occur due to the increased resistance to the ground potential, possibly causing interference with regard to the electromagnetic compatibility (EMC) of the entire converter.